RG-6... it's cheap, readily available, low loss, and easy to work with. Use it around here for just about everything.
Costs less than .10/ft and have even scored it for free. The gel filled stuff is for direct bury but is more expensive and messy to work with.
IHMO, for hobby use, the general purpose cable will be fine in the ground as long as the outer jacket isn't damaged.
Just slit the turf and stick it in the ground an inch or two.
However, always call the utility cable locator before digging.
For example, the phone and cable guys use the same shallow technique...
you don't want to hit anything.
Also, be aware if there are underground lawn sprinklers those pipes and wires can be very shallow buried.